DIFFERENTIAL EXPRESSION OF PROTEINS IN MUSCLE AND ELECTRIC ORGAN, A MUSCLE DERIVATIVE

The electric organ of electric fish develops from a myogenic lineage. We have used immunohistochemistry and immunoblotting to determine whic h features of the muscle phenotype are retained and whether any new on es are expressed in mature electrocytes of the electric fish Sternopyg us. The muscle-specific intermediate filament desmin was found through out the electrocytes, and different desmin antibodies detected molecul es with different subcellular distributions. Western blots confirm tha t these antibodies recognize a protein of MW = 53 kD, the molecular we ight of desmin. Other muscle proteins were also present within electro cytes: Actin and sarcomeric alpha-actinin were found within the subsyn aptic membrane beneath the plasmalemma of the electrocytes, and talin and acetylcholine receptors were detected both at the innervated poste rior face and at the non-innervated anterior face. This was confirmed using rhodamine-conjugated alpha-bungarotoxin. Neither myosin heavy ch ain nor tropomyosin was present in electrocytes. Finally, we detected within electrocytes a type I acidic keratin that forms a filamentous m eshwork within each cell. Immunoblots corroborate this result: A kerat in-positive doublet of MW = 50 kD and 57 kD was found in both electroc ytes and skin. Myosin, actin, talin, tropomyosin, desmin, alpha-actini n, and acetylcholine receptor, but not keratin, were all expressed in fish skeletal muscle fibers. Thus, electrocytes retain some muscle-spe cific proteins, do not express others, and in addition, express a non- muscle protein. (C) 1996 Wiley-Liss, Inc.